Here is what I found on http://whaleman.org/save_dolphins.htm:
Every year, over 20,000 dolphins and porpoises are killed by Japanese fisherman. After driving pods of wild dolphins from the open sea into shallow coves with motorized boats and loud bang sticks, the fishermen kill the dolphins, slashing their throats with knives or stabbing them with harpoon-like spears. Thrashing about, many of the dolphins take several minutes to die an agonizing cruel death, turning the surrounding sea blood red.
This brutal massacre, the largest dolphin kill in the world, goes on for six months of every year, from October through April.
Here is one of may youtube videos: